An underreamer includes one or more cutter blocks that expand radially-outward to increase the diameter of a wellbore when the underreamer is actuated from a retracted state to an expanded state. More particularly, the underreamer may include a sleeve that moves axially from a first position to a second position. The sleeve obstructs an opening in the body of the underreamer when in the first position and allows fluid flow through the opening when in the second position. When the sleeve is in the second position, fluid flows through the opening and exerts a hydraulic force on a piston, causing the piston to move the cutter blocks into the expanded state.
As the sleeve accelerates into the second position, the sleeve may contact a stationary component (e.g., a shoulder) in the body of the underreamer, which halts further axial movement of the sleeve. The resulting impact between the sleeve and the shoulder, however, may subject portions of the sleeve to a high plastic deformation. More particularly, the sleeve may have one or more radial ports or openings formed therethrough, and the impact may subject the portion of the sleeve proximate the openings to a large plastic strain. This may cause the portion of the sleeve proximate the openings to deform, which may inhibit the function and prevent further use of the underreamer.
What is needed, therefore, is an improved system and method for reducing plastic deformation and improving the reliability of impacting components in a downhole tool.